1. Field of the Invention
The present invention relates to a display apparatus. In particular, the present invention relates to a display apparatus including a plurality of pixel circuits each having display devices, transistors for drive and transistors for control.
2. Description of Related Art
A method for performing a drive with a constant electric current is known as a drive circuit. For example, as a light emitting device suitable for being driven by an electric current, a light emitting device (hereinafter referred to as an LED), an organic electroluminescent device (hereinafter referred to as an organic EL device or as an OEL device), and the like can be cited. The characteristics of these light emitting devices scarcely depend on temperature, and an emission intensity curve almost linear to an electric current can be obtained. Consequently, a method of a constant electric current drive has been proposed.
In the following, an organic EL device is exemplified, and a conventional electric current drive for light emission is described.
The organic EL device is featured by planar self emitting light from a thin film stocked layer capable of high intensity emission. The organic EL device can realize high efficient light emission at a low voltage by increasing the number of function stacked layers of organic layers, see “Applied Physics Letters”, U.S., 1987, Vol. 51, p. 913, “J. Applied Physics”, U.S. 1989, Vol. 65, p. 3610. As described above, because the organic EL device is driven to emit light by a constant electric current, some constant electric current driving schemes have been proposed.
For example, a drive circuit as shown in FIG. 3 has proposed in Japanese Patent Application Laid-Open No. 2001-056667 and U.S. Pat. No. 6,229,506. The drive circuit copies an input electric current (idata) to supply the electric current to OEL 13. The drive method is an electric current control type method of using an electric current as an input to set the electric potential of the control electrode of a transistor 11. The method has a technical advantage of the capability of supplying a substantially same electric current as an input electric current to the OEL 13 without being affected by the threshold value of the transistor 11 and a deteriorated voltage of the OEL 13.
Moreover, Japanese Patent Application Laid-Open No. S63-280300 discloses an information display apparatus arranging a plurality of display dots therein. Each of the display dots composed of collected light emitting diodes having different luminance colors. In particular, Japanese Patent Application Laid-Open No. S63-280300 discloses a configuration including a power supply for supplying a voltage to the light emitting diodes per each luminance color.
Moreover, Japanese Patent Application Laid-Open No. 2002-23666 discloses a plurality of configurations of an electronic display apparatus using cathode common type LED's emitting a plurality of color beams. One of the configurations uses an independent switching power supply outputting different DC voltages to respective colors. The other configuration uses a combination of simple power supply circuits for voltage adjustment.
Moreover, Japanese Patent Application Laid-Open No. H10-232649 discloses a configuration in which selection transistors and drive transistors are controlled by binary signals of on/off respectively, and in which peculiar voltage values or electric current values are variably output from a variable drive power supply during each sub-frame period.